1. Technical Field
This invention pertains to gas or liquid seals in general, and to brush seals in particular.
2. Background Information
Brush seals, consisting of a plurality of bristles sandwiched between a pair of backing plates, are a known means for sealing between a stationary element and a rotating element. The seal backing plates are attached to one of the stationary or rotating element and the bristles extend outwardly toward the other of the stationary or rotating element. The bristles are typically arranged in parallel rows with one end of the bristles captured between the backing plates and the other end extending outwardly. In some cases, the backing plates are centered on the bristles, and the ends of the bristles extend outwardly in opposite directions. The bristles extending between the two elements inhibit or prevent gas/fluid flow between the two elements.
The packing arrangement of the bristles, and their orientation between the elements determine some of the sealing characteristics of the seal. For example, bristles of varying stiffness can be used in the same seal to decrease the leakage rate through the seal; e.g., larger diameter bristles can be dispersed amongst smaller diameter bristles. The larger diameter bristles increase the aggregate bristle stiffness, and the intermingled smaller diameter bristles “fill in” the area between the larger bristles and minimize or prevent leakage. Bristles may also be skewed from one surface to accommodate disparate growth between the two surfaces. Skewing the bristles sometimes allows bristles to elastically deflect, rather than plastically deform, as one surface draws near the other.
Brush seals within gas turbine engines are most often manufactured from metallic bristles and backing plates. Metallic bristles are attractive because they provide a relatively effective seal in a cost effective manner that can be used in moderately high temperature environments. There are applications, however, where physical limitations make metallic bristles brush seals a less attractive option. Specifically, in applications where weight is a concern, it may be a disadvantage to implement a metallic seal. In other applications, metallic bristles may be susceptible to excessive wear. In still other applications, the temperature environment may be above that allowable for metallic bristles. In those instances, it may be advantageous to implement brush seals having ceramic, or ceramic like, bristles.
The methods used for manufacturing most metallic brush seals generally cannot be used for manufacturing ceramic brush seals, however. The bristles and backing plates of metallic brush seals are commonly joined by a bead of weld drawn between the backing plates. Ceramic type bristles, conversely, cannot be joined by a welding process. What is needed, therefore, is a practical and cost effective method of manufacturing ceramic, or ceramic like, bristle brush seals.